"The science behind climate change is settled, and human activity is responsible for global warming," Jackson told the Senate Environment and Public Works Committee. "That conclusion is not a partisan one."

Jackson's comments came as the Senate panel scrutinized President Obama's $10 billion budget request for EPA. The administration's fiscal 2011 proposal would cut the agency's total funding by about $300 million from 2010 levels while allotting $56 million -- including $43 million in new funding -- for regulatory programs to curb greenhouse gas emissions.

Senate Republicans used the hearing as a platform to blast EPA over its plans to begin rolling out greenhouse gas regulations next month after it determined last year that the heat-trapping emissions endanger human health and welfare.

Sen. James Inhofe (R-Okla.), the panel's ranking member, called on EPA to reconsider that determination after recent reports have revealed errors in the reports from the Intergovernmental Panel on Climate Change (IPCC) that were used to underpin EPA's finding and a recent controversy surrounding e-mails stolen from climate scientists that some have dubbed "Climategate."

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"We've been told that the science still stands," Inhofe said. "We've been told that the IPCC's mistakes are trivial. We've been told that Climategate is just gossipy e-mails between a few scientists.

"But now we know there's no objective basis for these claims," he added. "Furthermore, Climategate shows there's no 'consensus;' the science is far from settled."

Committee Republicans released a report today detailing concerns over the content of the e-mails that were lifted last year from computers at the Climatic Research Unit of the University of East Anglia, a research institute whose studies help form the basis of the IPCC reports.

Some of the e-mails reveal frustration with attacks from global warming skeptics, and opponents of greenhouse gas regulations have pointed to several of the exchanges as proof that scientists intentionally withheld climate data.

The Obama administration, as well as the majority of climate scientists and Democratic lawmakers, have maintained that nothing in the e-mails upends the scientific consensus that man-made emissions are contributing to climate change.

Jackson said that although science "can be a bit messy, the dust will settle" and that she has not seen anything at this point to show that the endangerment finding is not on solid ground.

"I do not agree that the IPCC has been totally discredited in any way," Jackson said, adding that it is important to understand that the IPCC is a body that follows open and impartial practices.

"Let me be very clear," said Sen. Barbara Boxer (D-Calif.) the committee chairwoman. "The majority of this committee believes in strong numbers that we must act," on global warming, she added.

Sen. Bernie Sanders (I-Vt.) angrily blasted his Republican colleagues for their implications that global warming science had not been settled. "This country faces many many problems, not the least of which, we have national leaders rejecting basic science," Sanders said. "I find it incredible, I really do, that in the year 2010 on this committee, there are people who are saying there is a doubt about global warming. There is no doubt about global warming."